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From:   Jisheng Zhang <Jisheng.Zhang@synaptics.com>
To:     Catalin Marinas <catalin.marinas@arm.com>,
        Will Deacon <will@kernel.org>,
        Steven Rostedt <rostedt@goodmis.org>,
        Mark Rutland <mark.rutland@arm.com>
CC:     "linux-arm-kernel@lists.infradead.org" 
        <linux-arm-kernel@lists.infradead.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        Torsten Duwe <duwe@suse.de>
Subject: Re: [PATCH 1/3] ftrace: introdue ftrace_call_init
Thread-Topic: [PATCH 1/3] ftrace: introdue ftrace_call_init
Thread-Index: AQHVVoEOXDxpF53mfUS1paE9VVhs/acCUvOA
Date:   Mon, 19 Aug 2019 11:30:38 +0000
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        <20190819191622.57050fdf@xhacker.debian>
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On Mon, 19 Aug 2019 19:16:22 +0800 Jisheng Zhang wrote:

> On some arch, the FTRACE_WITH_REGS is implemented with gcc's
>  -fpatchable-function-entry (=3D2), gcc adds 2 NOPs at the beginning
> of each function, so this makes the MCOUNT_ADDR useless. In ftrace
> common framework, MCOUNT_ADDR is mostly used to "init" the nop, so
> let's introcude ftrace_call_init().
>=20
> Signed-off-by: Jisheng Zhang <Jisheng.Zhang@synaptics.com>
> ---
>  include/linux/ftrace.h | 1 +
>  kernel/trace/ftrace.c  | 4 ++++
>  2 files changed, 5 insertions(+)
>=20
> diff --git a/include/linux/ftrace.h b/include/linux/ftrace.h
> index 8a8cb3c401b2..8175ffb671f0 100644
> --- a/include/linux/ftrace.h
> +++ b/include/linux/ftrace.h
> @@ -458,6 +458,7 @@ extern void ftrace_regs_caller(void);
>  extern void ftrace_call(void);
>  extern void ftrace_regs_call(void);
>  extern void mcount_call(void);
> +extern int ftrace_call_init(struct module *mod, struct dyn_ftrace *rec);
> =20
>  void ftrace_modify_all_code(int command);
> =20
> diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
> index eca34503f178..9df5a66a6811 100644
> --- a/kernel/trace/ftrace.c
> +++ b/kernel/trace/ftrace.c
> @@ -2500,7 +2500,11 @@ ftrace_code_disable(struct module *mod, struct dyn=
_ftrace *rec)
>  	if (unlikely(ftrace_disabled))
>  		return 0;
> =20
> +#ifdef MCOUNT_ADDR
>  	ret =3D ftrace_make_nop(mod, rec, MCOUNT_ADDR);
> +#else
> +	ret =3D ftrace_call_init(mod, rec);
> +#endif

If we want to remove MCOUNT_ADDR from all arch, I could cook patches for
this.